The proposed research is concerned with the mechanism by which rodents regulate energy balance so as to maintain a reasonably stable body weight and composition. One of the hypotheses to be examined proposes that the nutritional state of the animal modulates the sensitivity of the satiety system to enterogenous and postingestive satiety signals so as to correct nutritional deficits or dispose of nutritional excess. The mechanism by which such modulating signals are transmitted from the periphery to central nervous system receptors will be investigated as well as the nature of the satiety signals generated by the ingestive process. The nutritional and metabolic status of rats will be manipulated by means of various kinds of nutrient deprivation, force-feeding and administration of agents affecting carbohydrate, protein and fat metabolism. The effect of such manipulations on food-motivated behavior will be ascertained with the use of a variety of behavioral measures.